This invention relates to devices for cleaning pipelines and more particularly to pipeline pigs used for internal cleaning, corrosion control, and fluid separation in pipelines.
Pipeline pigs are used to accomplish various operations inside in-place pipeline systems, such as removing wax, dirt, and water accumulation from pipelines; separating products to reduce the amount of interface in the transition zone between different types of fluids flowing in pipelines; controlling liquids inside a pipeline, e.g., reducing liquid accumulations in two-phase flow pipelines, filling pipelines for hydrostatic tests, dewatering pipe-lines following hydrostatic tests, drying operations, and purging hydrostatic test water with petroleum liquid; inspecting pipelines and detecting dents, buckles, or excessive corrosion; and applying internal coatings to the walls of pipelines for corrosion protection.
Traditionally, spheres, metal-bodied pigs plastic-bodied pigs, and foam pigs have been used to accomplish the above listed operations. The effective use of each of these prior pigs is usually limited to specific applications. There has been little overlap in the effective use of the prior pigs. As a result, no single pipeline pig is known which will accommodate and fulfill the various needs and uses for pipeline pigs.
Problems also arise in the use of the known pipeline pigs. For example, if the pipeline has any 90.degree. bends or elbows a special pig, such as a sphere or foam pig, has traditionally been used. In some circumstances, these pigs do not clean or scrape the inside of the pipeline as well as steel-bodied pigs. If the bend is made using a screwed 90.degree. fitting a foam pig cannot be used, as such screwed fittings will normally destroy a foam pig. Also, a foam pig often turns sideways as it passes through an elbow, which greatly reduces the effectiveness of the foam pig.
A similar problem arises if the pipeline has restrictions such as reduced port valves, venturi valves, plug valves, etc. In these cases, again, a foam pig must be used.
Therefore, there is a need for a universal pipeline pig which will adapt to most known pipeline configurations; which will pass through most types of 90.degree. bends, elbows, and other pipe fittings; which will pass through check valves, venturi valves, plug valves, pipeline tees, etc.; and which will transport a variety of cleaning, maintenance, and information gathering equipment through a pipeline.